after digging several situation and testimonials from customer, it's probably ESD that damages the gyro charge pump leading to either silent or crazy gyro. You can try to remove the gyro cap (pointed where it's currently written 14V, where 8-10v should rather be seen).
My conclusion is that people discharge ESD in the capacitor or in the switches when manipulating (killing the act or aux pad internal pullup resistor).
The fw has been ruled out as it writes properly in the sensor registers and init goes perfect, even reading back from the sensor work, just the internal MEMS is damaged.